So, last night, I disassembled a set of 4.3 heads and started a picture sequence of head modification, I will try and do one major step each week amongst my other responsibilites in life. Note that I painted the combustion chambers florescent orange, I did this with the hope that it will contrast well with machining, not my usual machining dye.
The first thing I always do is run the appropriate bottoming taps into all the blind holes and regular taps into the through-holes.
Machining Exhaust Valve Reliefs, Unshrouding Combustion Chamber.
The stock exhaust valve is badly shrouded by the wall of the combustion chamber, I am putting a 1.60 inch exhaust valve in this head so I am opening up the side walls to give better flow. I use a valve guide centered pilot and a specially cut stellite grinding stone.
A 2 1/4 inch diameter stellite stone is cut with an in-house made diamond tool to give it a 3/8 round contour on the bottom and it is slowly feed down into the combustion chamber until it is cut to a set depth which is 0.050 above the existing exhaust seat. This is not the final cut, when the valve guides are replaced and the new seat is cut an addition cut is made to the final depth. This stone and the bottom shape almost entirely cleans up that area but there is always a little hand work to do.
A mask and safety sheild must be worn as the stone dust if very irritating to the sinus, lungs and throat. The grinders can go up to 12,000 rpm and a chest protector and full face sheild must be worn.
The cut takes the relief to about 0.010 from the edge of the cylinder head gasket.
Please click on the picture and enlarge it so that you can see the extent that the area has been opened up.
Next, opening up the Intake Valve Shrouding.
Great Pic. So how much material did you remove? How much bigger in size will the chamber end up. I think Vortecs are 64cc from GM, arent they?
